The requirements of biomass pellet machine for raw materials directly affect the molding quality, production efficiency and equipment life of pellets, and are the core prerequisite for ensuring stable production. Different types of biomass pellet machines (such as ring die pellet machines and flat die pellet machines) have slightly different requirements for raw materials, but they can be generally summarized into the following key indicators:

1. Raw material types: must have "compressibility" and "fibrousness"

The raw materials of biomass pellet machines are mainly agricultural and forestry wastes, but not all wastes are suitable. They must meet the characteristics of high fiber content and rich lignin (lignin is a natural "adhesive" that softens and bonds the fibers together when extruded at high temperatures):

Applicable raw materials:

Agricultural waste: straw (corn stalks, wheat stalks, rice stalks), rice husks, peanut shells, cottonseed shells, etc. (fiber content 30%-50%);

Forestry waste: wood chips (pine, fir, poplar, etc.), branches, bark, sawdust (lignin content 20%-30%);

Others: sugarcane bagasse, Chinese medicine residue, mushroom stick waste (impurities need to be removed and the fiber structure is complete).

2. Moisture content of raw materials: core control index (15%-20%)

Moisture content is a key factor affecting particle forming. Too high or too low will lead to production problems:

Moisture content is too high (>20%):

Molding is difficult: the material is easy to stick to the pressing wheel and the inner wall of the mold, resulting in "mold blocking" phenomenon, and the particles are loose and easy to break;

Increased energy consumption: additional energy is required to dry the particles (natural drying is prone to mold);

Storage hazards: when the moisture content of the particles exceeds 15%, they are prone to agglomeration and mold after storage for more than 1 month, and the calorific value decreases by 10%-15%.

Moisture content is too low (<15%):

Increased fiber brittleness: the fiber is easy to break during extrusion, the particle strength is insufficient, and it is easy to crush (the finished product breakage rate exceeds 10%);

Intensified equipment wear: the friction between the dry material and the mold increases, and the mold life is shortened by more than 30% (such as the ring mold life is reduced from 800 hours to 500 hours).

Control method:

During the pretreatment stage, the moisture content of the raw materials is reduced from the natural state (straw is about 30%-40%, sawdust is about 40%-50%) to 15%-20% through drying equipment (such as drum dryer);

Different raw material benchmarks: the moisture content of sawdust can be slightly lower (15%-18%), and the moisture content of straw can be slightly higher (18%-20%, because the straw fiber is coarse and needs more water to soften).

3. Raw material particle size: need to match the mold aperture (2-5mm)

The particle size of the raw material after crushing needs to match the mold aperture of the pellet machine (the mold aperture is usually 6-12mm), general requirements:

Particle size after crushing: more than 90% of the material particles must have a diameter of <3mm and high uniformity (avoid large particles).

If the particle size exceeds 5mm: it is easy to cause the mold hole to be blocked, the pressure wheel to be unevenly stressed, and even stop;

If the particle size is too fine (<1mm): the material is easy to "slip", cannot be effectively extruded, and will also increase dust pollution.

Crushing requirements for different raw materials:

Straw: Due to the long fiber (corn stalk fiber can reach 50mm), it needs to be crushed twice (first coarsely crushed to 10mm, then finely crushed to 3mm);

Wood chips: Sawdust is usually less than 3mm, and only large impurities need to be screened to remove;

4 Raw material impurities: Strictly control the "foreign matter content"

Impurities in the raw materials (metal, stone, plastic, etc.) will directly damage the equipment and need to be removed in advance:

Metal impurities: such as iron wire and nails in field straw, staples in wood chips, etc., need to be removed by magnetic separation equipment, otherwise they will scratch the inner hole of the mold or break the pressure wheel shaft.

Large foreign matter: such as plastic film, glass fragments, stones, etc., need to be screened through a vibrating screen (sieve hole 5-10mm) to avoid entering the pelletizing system and causing jamming.

Ash control: The raw material ash content (residue left after combustion) needs to be less than 5% (such as rice husk ash is about 12%, which needs to be mixed with wood chips to reduce the ash content), otherwise the pellets are easy to coke during combustion, affecting the efficiency of the boiler.

Summary: The "gold standard" of high-quality raw materials

Type: fibrous agricultural and forestry waste (without oil, high impurities);

Moisture content: 15%-20% (error does not exceed ±2%);

Particle size: 2-5mm (uniform without large pieces);

Impurities: no metal, stone, plastic, ash content <5%;

Pretreatment: uniform crushing + moderate conditioning.

Raw materials that meet these requirements can make the biomass pellet machine's forming rate (qualified pellet ratio) reach more than 95%, pellet density ≥1.1g/cm³, crushing strength >90% (drop test crushing rate <10%), while extending the equipment life by more than 30% and reducing the overall production cost.